Step-up/step-down type DC-DC converter, and control circuit and control method of the same
View Patent ↗To provide a control circuit and control method of a step-up/step-down type DC-DC converter capable of realizing high efficiency. In a state ( 1 ), a terminal Tx of a choke coil L 1 is connected to an input terminal Tin, and a terminal Ty is connected to a reference potential. In a state ( 2 ), the terminal Tx is connected to the reference potential, and the terminal Ty is connected to an output terminal Tout. In the state ( 3 ), the terminal Tx is connected to the input terminal Tin, and the terminal Ty is connected to the output terminal Tout. A first period operation TO 1 is constituted by the states ( 1 ) and ( 2 ), and a second period operation TO 2 is constituted by the states ( 1 ) and ( 3 ). A second period T 2 , in which the second period operation TO 2 is performed, is a value n times as long as a first period T 1 , in which the first period operation TO 1 is performed. In the second period operation TO 2 , the state ( 1 ) is switched to the state ( 3 ) so that an increasing slope of an inductor current IL is reduced.
1. A control method of a step-up/step-down type DC-DC converter including: a first switching element connected between a voltage input terminal and one terminal of an inductance element; a first rectifying element connected between a reference potential and one terminal of the inductance element; a second rectifying element connected between a voltage output terminal and the other terminal of the inductance element; and a second switching element connected between the reference potential and the other terminal of the inductance element, the method comprising:
setting either one of a first state and a second state in a first cycle and, in case that the first state is set, switching from the first state to the second state when current of the inductance element reaches a given value in the first cycle; and
setting the first state in a second cycle following the first cycle and switching from the first state to a third state when current of the inductance element reaches the given value in the second cycle,
wherein in the first state, the first and second switching elements are ON;
wherein in the second state, the first and second switching elements are OFF;
wherein in the third state, the first switching element is ON and the second switching element is OFF;
wherein the first cycle includes a consecutive sequence of the first state and the second state, or includes the second state; and
wherein the second cycle includes a consecutive sequence of the first state and the third state.
2. The control method of the step-up/step-down type DC-DC converter according to claim 1 , wherein
the second cycle is n (n: a real number of one or more) times as long as the first cycle.
3. The control method of the step-up/step-down type DC-DC converter according to claim 2 , wherein
the n is a natural number of 2 or more.
4. The control method of the step-up/step-down type DC-DC converter according to claim 1 , wherein
the first rectifying element is a third switching element,
the second rectifying element is a fourth switching element,
the third and fourth switching elements are OFF in the first state,
the third and fourth switching elements are ON in the second state, and
the fourth switching element is ON, and the third switching element is OFF, in the third state.
5. A control circuit of a step-up/step-down type DC-DC converter, comprising:
a first switching element connected between a voltage input terminal and one terminal of an inductance element;
a first rectifying element connected between a reference potential and one terminal of the inductance element;
a second rectifying element connected between a voltage output terminal and the other terminal of the inductance element;
a second switching element connected between the reference potential and the other terminal of the inductance element; and
a control part for controlling: a first state where the first and second switching elements are ON; a second state where the first and second switching elements are OFF; and a third state where the first switching element is ON and the second switching element is OFF, wherein either one of the first state and the second state is set in a first cycle and, in case that the first state is set, the first state is switched to the second state when current of the inductance element reaches a given value in the first cycle, and wherein the first state is set in a second cycle following the first cycle and the first state is switched to the third state when current of the inductance element reaches the given value in the second cycle;
wherein the first cycle includes a consecutive sequence of the first state and the second state, or includes the second state; and
wherein the second cycle includes a consecutive sequence of the first state and the third state.
6. The control circuit of the step-up/step-down type DC-DC converter according to claim 5 , the converter further comprising:
a third switching element as the first rectifying element, and
a fourth switching element as the second rectifying element,
wherein the control part turns the third and fourth switching elements OFF in the first state, turns the third and fourth switching elements ON in the second state, and turns the fourth switching element ON and the third switching element OFF in the third state.
7. A step-up/step-down type DC-DC converter comprising:
a first switching element connected between a voltage input terminal and one terminal of an inductance element;
a first rectifying element connected between a reference potential and one terminal of the inductance element;
a second rectifying element connected between a voltage output terminal and the other terminal of the inductance element;
a second switching element connected between the reference potential and the other terminal of the inductance element; and
a control part for controlling: a first state where the first and second switching elements are ON; a second state where the first and second switching elements are OFF; and a third state where the first switching element is ON and the second switching element is OFF, wherein either one of the first state and the second state is set in a first cycle and, in case that the first state is set, the first state is switched to the second state when current of the inductance element reaches a given value in the first cycle, and wherein the first state is set in a second cycle following the first cycle and the first state is switched to the third state when current of the inductance element reaches the given value in the second cycle;
wherein the first cycle includes a consecutive sequence of the first state and the second state, or includes the second state; and
wherein the second cycle includes a consecutive sequence of the first state and the third state.
8. A control circuit of a step-up/step-down type DC-DC converter comprising:
a first switching element connected between a voltage input terminal and a first terminal of an inductance element, the first switching element including an inverse parallel diode which is conductive in a direction from the first terminal of the inductance element to the voltage input terminal;
a second switching element connected between a reference potential and the first terminal of the inductance element;
a third switching element connected between the reference potential and the second terminal of the inductance element;
a fourth switching element connected between a voltage output terminal and the second terminal of the inductance element;
a soft-start control circuit for outputting a soft-start signal to step-up or step-down as time passes;
an error amplifier for amplifying an error between a reference voltage to determine set voltage of an output voltage or the soft-start signal, whichever is lower, and the output voltage; and
a switching circuit, during a term where the output voltage is lower than the input voltage, alternately switching a first state where the first and third switching elements are ON and a second state where the second and fourth switching elements are ON depending on an output from the error amplifier, and during a term where the output voltage is higher than the input voltage, the switching circuit alternately switching the third switching element and the fourth switching element depending on an output from the error amplifier with the first switching element and the second switching element being set ON and OFF, respectively;
wherein the soft-start signal is at least one of,
a) a control signal to make the output voltage gradually step-up to a predetermined voltage when the DC-DC converter starts up, and
b) a control signal to make the output voltage gradually step-down to a zero voltage when the DC-DC converter terminates.
9. The control circuit of the step-up/step-down type DC-DC converter according to claim 8 , wherein the switching control circuit comprises:
a control signal generating circuit for outputting a control signal having pulse width depending on level of the output signal from the error amplifier;
a comparator for comparing the output voltage and the input voltage;
a mask circuit, depending on a result obtained by the comparator, allowing the control signal to pass during the term where the output voltage is lower than the input voltage, and masking the control signal during the term where the output voltage is higher than the input voltage.
10. The control circuit of the step-up/step-down type DC-DC converter according to claim 9 , wherein an output from the comparator is set to low-level during the term where the output voltage is higher than the input voltage, and the mask circuit is an AND circuit.
11. The control circuit of the step-up/step-down type DC-DC converter according to claim 8 , wherein the error amplifier comprises:
a first terminal which the output voltage is inputted to and has a first polarity;
a second terminal which the reference voltage inputted to and has a second polarity;
a third terminal which the soft-start signal is inputted to and has the second polarity.
12. The control circuit of the step-up/step-down type DC-DC converter according to claim 9 , wherein the error amplifier comprises:
a first terminal which the output voltage is inputted to and has a first polarity;
a second terminal which the reference voltage inputted to has a second polarity;
a third terminal which the soft-start signal is inputted to and has the second polarity.
13. The control circuit of the step-up/step-down type DC-DC converter according to claim 10 , wherein the error amplifier comprises:
a first terminal which the output voltage is inputted to and has a first polarity;
a second terminal which the reference voltage inputted to and has a second polarity;
a third terminal which the soft-start signal is inputted to has the second polarity.
14. A control method of a step-up/step-down type DC-DC converter including: a first switching element connected between a voltage input terminal and a first terminal of an inductance element; a second switching element connected between a reference potential and the first terminal of the inductance element; a third switching element connected between the reference potential and the second terminal of the inductance element; and a fourth switching element connected between a voltage output terminal and the second terminal of the inductance element, the method comprising:
setting the first through fourth switching elements OFF;
repeating a consecutive sequence of a first state where the first and third switching elements are set ON and a second state where the second and fourth switching elements are set ON alternately, in response to a start-up command; and
keeping the first switching element and the second switching element ON and OFF, respectively, when the output voltage becomes higher than the input voltage, and alternately repeating ON-setting of the third switching element and ON-setting of the fourth switching element.
15. A step-up/step-down type DC-DC converter comprising:
a first switching element connected between a voltage input terminal and a first terminal of an inductance element, the first switching element including an inverse parallel diode which is conductive in a direction from the first terminal of the inductance element to the voltage input terminal;
a second switching element connected between a reference potential and the first terminal of the inductance element;
a third switching element connected between the reference potential and the second terminal of the inductance element;
a fourth switching element connected between a voltage output terminal and the second terminal of the inductance element;
a soft-start control circuit for outputting a soft-start signal to step-up or step-down as time passes;
an error amplifier for amplifying an error between a reference voltage to determine set voltage of an output voltage or the soft-start signal, whichever is lower, and the output voltage; and
a switching circuit, during a term where the output voltage is lower than the input voltage, alternately switching a first state where the first and third switching elements are ON and a second state where the second and fourth switching elements are ON depending on an output from the error amplifier, and during a term where the output voltage is higher than the input voltage, the switching circuit alternately switching the third switching element and the fourth switching element depending on an output from the error amplifier with the first switching element and the second switching element being set ON and OFF, respectively;
wherein the soft-start signal is at least one of,
a) a control signal to make the output voltage gradually step-up to a predetermined voltage when the DC-DC converter starts up, and
b) a control signal to make the output voltage gradually step-down to a zero voltage when the DC-DC converter terminates.